In 2004 the World Health Organisation reported the top five causes of visual impairment (VI) and blindness worldwide as (1) Cataract, (2) Glaucoma, (3) Age Related Macular Degeneration (AMD), (4) Corneal opacities and (5) Diabetic Retinopathy (DR). Globally, the number of people of all ages with VI is 285 million. The initiative Vision 2020 has largely focussed on the elimination of cataract due to its amenability to cure through surgery.
Approximately 80% of blindness is preventable or curable. The majority (90%) of those blind worldwide live in low-income countries. Human and technological resources for the provision of eye care follows the Inverse Care Law, i.e. where the majority of the blind people live, are the least existing resources, and conversely; in areas of low blindness, high provision of resources exist. To create sustainable health services, accurate and representative data needs to be collected about VI so that policy makers can distribute limited resources in a manner that maximizes patient benefit and also so that planning for future requirements and infrastructure can be determined.
In low-income countries there are insufficiently trained personnel and a lack of ophthalmic equipment for the detection of potentially blinding conditions. This means many people do not receive the necessary eye treatment and so are left with vision impairment.
Cost is the main hurdle to providing the ophthalmic equipment in these settings, because the equipment is large, complex and costly. Moreover, even if ophthalmic equipment is available there are often logistical constraints associated with transporting this equipment across large distances in what is often environmentally hostile terrain. The training of specialised personnel is also costly and even when trained there are often not enough specialists available to cover the area or population to be screened.
Global loss in productivity as a result of VI is thought to be 121 billion US$, thus there is an invidious spiralling decline in healthcare as VI increases. Given that 80% of blindness is preventable or curable if detected early enough, it follows that a sensible eye care strategy can positively affect not only the wellbeing of each individual but also a population or country as a whole increasing not only health but GDP and so the ability to yet further improve healthcare.
In the developed world, whilst eye care is available, especially for individuals who are able to visit an opticians or an ophthalmologist, it is costly and with an expanding population there is an ever increasing desire to undertake healthcare in the most efficient and effective way possible. Thus there is also a need within the developed world to improve healthcare so that more individuals can be effectively treated per unit investment.
Moreover, there is also a need to be able to take healthcare into various communities such as schools, retirement homes, and prisons, the prerequisite for which is the development of portable devices which are easy to use by trained but not necessarily experienced or senior staff.
In the medical examination of the eye, the visualisation of the retina through the pupil (ophthalmoscopy) is performed on a routine basis. This is done, in routine testing, through an instrument called a “direct ophthalmoscope”. It is a pen-sized (approximately 20 cm) viewing system held by a doctor in front of the patient's eye, often at very close face-to-face distance. Such an instrument is simple, relatively inexpensive, yet rather difficult to use. In the western world, training is typically undertaken at undergraduate level within optometry and medicine. The field of view is very small (5 degrees at best), the aiming is critical and the focussing requires great manual dexterity. Moreover, the segmentation of the image in to very small fields requires the operator to look at a small portion of the retina at a time, and to reconstruct a “mental image” of the retina itself.
To overcome these limitations, a more expensive instrument can be used. It is called an “indirect ophthalmoscope”. It consists of a short-focal-length lens (known in the practice as “superfield”), which the doctor holds in front of the patient's eye, and a headpiece, which carries a viewer that projects light through the lens, or superfield, into the eye. The user aligns by hand the lens, the eye and the viewer, and looks at the retina. The field of view is much wider than a direct ophthalmoscope (40 degrees). However, the system is expensive and the use can be difficult due to the intrinsically delicate manual alignment. Proficiency in this technique is typically limited to post-graduate ophthalmology sub-specialist doctors.
Two further instruments are derived from the indirect ophthalmoscope: a fundus camera and a panoptic ophthalmoscope. In the “fundus camera”, an indirect ophthalmoscope is pre-aligned. The patient's head is immobilised through a head-and-chin rest, and a photograph is taken through the pre-aligned, indirect ophthalmoscope using a camera. The panoptic ophthalmoscope is a proprietary instrument. This indirect ophthalmoscope is pre-aligned, and held by a doctor as a single unit in front of the patient's eye. The user observes the retina through the instrument. A camera can be attached to the device.
Attempts have been made to build ophthalmoscopes by using small digital cameras (e.g. webcams) either attached to an ophthalmoscope, or held directly in front of a patient's eyes, with an associated set of prisms, including refraction compensating lenses, to project light into the eye, in order to provide the necessary illumination. Unfortunately, the results have been disappointing because the size of the prisms causes either a gross reduction of the field of view or poor resolution and focus.
With the above in mind we have developed an ophthalmoscope based on an autofocussing miniature camera typically a smartphone camera. Alternatively, the camera can avoid autofocussing if the depth of field is long enough for example using a non-autofocusing, low-numerical aperture system is a way to improve the depth of focus. In other words, the system can be built to be “focus-free”, such as in inexpensive webcams. Whilst the use of smartphones to test for eye disorders is not new, indeed we have suggested the use of this technology in this particular discipline in the past (Journal of Mobile Technology in Medicine [JMTM] Vol. 1 issue 3 Sep. 2012 & Eye 2012, 26, 343-354) and others have commented favourably upon the idea (Ophthalmology Volume 119, Number 10, October 2012), no one has thought to use a smartphone for direct ophthalmoscopy and no one has produced a device which is simple, effective and reliable, which can visualise the fundus without substantial training and which offers a substantial field improvement on standard direct ophthalmoscopy, bringing the specifications close to indirect ophthalmoscopes or fundus cameras.